I did turn off the notifications for all fitness-related items, and I have in fact seen a marked improvement in battery life. I'm not getting estimates of about 28-30 hours just like you.

While I agree that the heartrate measurements probably don't take up much battery, I would think the step count measuring does. I guess I'm just astonished that it's impossible to turn those features off. Google Fit gives me the option to turn it off, but Moto's version does not. I can open the "Moto Body Steps" app and see how many steps I've taken during the day. I really wish I could turn that off, and/or have better control over what's running on my watch.